1. Field of the Invention
The present invention relates to a headrest to be mounted on a seat back of a vehicle seat, and in particular, the invention is directed to an improvement of the headrest which not only provides a reliable support for a head of seat occupant, but also provides a high absorption of an impact given to the seat occupant's head in case of a backward or rear-end collision or the like.
2. Description of Prior Art
In general, a headrest, adapted to be mounted on a seat back of vehicle seat, is comprised of a trim cover assembly, a foam padding and a pair of headrest stays. In most cases, in assembly of the headrest, a three-dimensional trim cover assembly is preformed, which conforms to a predetermined contour of the headrest, and a pair of spaced-apart headrest stays are also preformed by bending a tubular rod member in an inverted-U-shaped configuration so that a pair of rectilinearly extending rod portions thereof constitutes that particular pair of headrest stays. In this regard, so formed inverted-U-shaped rod member with two headrest stays defined therein is placed in the inside of the three-dimensional trim cover assembly in such a fashion that the two headrest stays extend outwardly from a bottom wall of the trim cover assembly, thereby providing a basic headrest unit. Such basic headrest unit is placed in a foaming die, after which, a liquid foaming agent is injected into the inside of the trim cover assembly and cured into an increased mass of foam padding filled therein. In that normal process of assembly, a resultant headrest is produced, in which the foam padding, overlaying a part of the inverted-U-shaped rod member, is effective in giving a cushony and resilient support for the head of seat occupant.
In the foregoing typical headrest, a horizontal rod portion of the inverted-U-shaped rod member (i.e. a transversely extending rod portion defined between the two headrest stays) serves to receive a great load applied from the head of seat occupant which is displaced thereto under backward inertia in the case of rear-end collision. Otherwise stated, when a rear-end collision occurs, the seat occupant's head is abruptly displaced and pressed against the headrest under the backward inertia thereof, while being forcibly sunk into the foam padding of the headrest. As a result thereof, an excessive great load thus applied from the head is received by the afore-said horizontal rod portion of inerted-U-shaped rod member, via a compressed local region of the foam padding.
In this regard, it is important that the seat occupant's head should be displaced to a proper head receiving area of the headrest in which the afore-said horizontal rod portion extends transversely thereof, so that a whole of excessive great load applied from the head is received by that horizontal rod portion.
Let us now assume that the seat occupant's head is displaced backwards to a point lower or above the horizontal rod portion, which means that the backward movement of head does not correspond to the above-defined proper head receiving area, when a rear-end collision occurs. In that case, it is highly possible that the head will be inclined excessively either backwardly or forwardly relative to the horizon rod portion.
Such problem is simply due to the fact that the proper head receiving area of headrest is narrow or small, because nothing but the horizontal rod portion receives the load applied from the seat occupant's head.
Thus, it is necessary to increase or widen such head receiving area in a vertical direction of the headrest. For that purpose, for example, the Japanese Laid-Open Patent Publication No. 2006-69286 suggests bending a horizontal rod portion of inverted-U-shaped rod member in a vertically extending configuration, such as a generally V-shaped configuration, within the headrest, and also suggests formation of a support bar between two vertically extending rod portions of that inverted-U-shaped rod member within the headrest. Accordingly, the head receiving area is increased in the vertical direction of headrest, thereby avoiding the possibility that the head will be inclined excessively either backwardly or forwardly relative to the horizontal rod portion in the case of rear-end collision.
However, according to the foregoing construction, it is certainly possible to prevent the excessive inclination of the seat occupant's head relative to the horizontal rod portion, but, when a rear-end collision actually occurs, the seat occupant's head will be forcibly pressed against and sunk deeply into the headrest at the widened head receiving area where the afore-said vertically bent rod portion or support bar lies. As a consequence thereof, the localized region of foam padding is greatly compressed between the head and such rod portion or support bar, to an excessively small degree at which the elastic repercussive force of that foam padding localized region no longer absorbs a corresponding impact energy given to the head.
To solve this problem, the foregoing Japanese prior art (2006-69286) suggests provision of a low-repercussive elastic material between the foam padding and the rod portion or support bar in order to absorb the impact energy. This arrangement however increases the weight of headrest as well as costs for assembly of the headrest.
Also, the Japanese prior art indicates another alternative arrangement that does not require such provision of low-repercussive elastic material, as shown in FIGS. 8 and 9, but, according thereto, a whole of impact energy caused is not absorbed by foam padding and therefore, a remaining portion of the impact energy, which is not absorbed by the foam padding, is imparted via the hard rod portion or hard support bar to the seat occupant's head. Thus, even in that alternative mode, there still remains the problem that the seat occupant's head will not be sufficiently protected against the impact energy in the case of rear-end collision or the like.